Crush-before-curing process for producing densified polyurethane foam



United States Patent O 3,506,600 CRUSH-BEFORE-CURING PROCESS FOR PRODUC- ING DENSIFIED POLYURETHANE FOAM Natale C. Zocco, East Haven, and Stanley I. Cohen, Orange, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Continuation-impart of abandoned application Ser. No. 708,524, Feb. 27, 1968. This application Nov. 29, 1968, Ser. No. 780,247

Int. Cl. C08g 53/08 U.S. Cl. 260-2.5 26 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of copending applications Ser. No. 708,524, filed Feb. 27, 1968, Ser. No. 661,756, filed Aug. 4, 1967, and Ser. No. 573,189, filed Aug. 18, 1966, all now abandoned.

This invention relates to a process for preparing flexible, densified polyurethane foams and to products produced thereby.

There is a great need at the present time for flexible synthetic materials useful as backing for floor coverings such as rugs and plastic tile, and for use as padding, cushions, mattresses and the like.

The preparation of polyurethane elastomers has been known for many years. U.S. Patent No. 2,866,774 discloses a technique for preparing polyurethane rubbers by reacting a polyether glycol of at least 600 molecular weight with an organic polyisocyanate. Although this type of polyurethane elastomer is somewhat flexible, the density is generally greater than about 40 pound per cubic foot and control of density is not easily obtained during processing. In addition, elastomers of this type generally must be prepared by batch-wise casting or molding rather than on a continuous basis.

Polyurethane foams meet the flexibility and cost requirements, but they do not meet the density, resiliency and durability requirements which make them suitable for such uses as backing for floor covering materials and the like. Attempts have been made to increase the density of flexible polyurethane foams, but the techniques employed and the results obtained have been unattractive for various reasons.

Thus, U.S. Patent 3,298,976 discloses that flexible polyurethane foams having densities from about 3.0 to 4.2 pounds per cubic foot can be prepared by incorporating particles of barytes in the polyurethane forming reaction mixture. However, in addition to requiring an added ingredient, such polyurethane foams are unsuitable in applications where denser, flexible polyurethane foams are desired.

Polyurethane foams having a density of from about 25 to about 50 pounds per cubic foot have been made by a critical molding technique as described in U.S. Patent 3,506,600 Patented Apr. 14, 1970 ICC 3,125,617. While these foams may be suitable for some such uses as rug padding.

It is also known that'crushing polyurethane foams without a long curing period causes permanent densification of the center portion of the foam, rendering the entire piece unusable. This undesirable effect is reported in M0- bay Chemical Company Technical Information Bulletin No. 38Fl4, dated Nov. 25, 1959. U.S. Patents 3,060,137 and 3,012,283 also disclose certain crushing techniques for polyurethane foams.

Now it has been found, in accordance with this invention, that selected, flexible, densified polyurethane foams can be prepared by employing a combination of critical interrelated process steps as defined hereinafter. The process of this invention is economical and thus is attractive for commercial operations, particularly in the continuous embodiments thereof. Furthermore, the flexible, densified polyurethane foams provided by this process are characterized by superior physical properties and have numerous commercial applications.

More specifically, it has been found that densified polyurethane foams having a density between about 1.5 and about 15 pounds per cubic foot, and preferably between about 1.5 and about 10 pounds per cubic foot, can be prepared by allowing a polyurethane foam-forming reaction mixture having a free rise density between about 0.8 and about 4.0 pounds per cubic foot to rise, thereby forming a partially cured cellular material; maintaining the partially cured cellular material for a critical period of time at a critical environmental temperature and applying a compressive force to the partially cured cellular material to reduce its volume by a specified amount. By the term free rise density in the claims and specification herein is meant the density a polyurethane foam would have if the foam-forming reaction mixture were allowed to rise and cure without the application of a compressive force.

Since densification begins around the middle of the partially cured cellular material, in some embodiments outer layers of less dense flexible polyurethane foam may be present. Such materials are useful for many applications; alternately, they can be trimmed to remove the less dense exterior layers. Where densified polyurethane foams having outer layers of less dense polyurethane foam are provided, the term a flexible, densified polyurethane foam in the claims and specification herein refers to the densified layer. However, it is to be understood that the process of this invention pertains to the manufacture of flexible, densified polyurethane foams both with and without the aforementioned less dense exterior layers.

The densified foams provided according to the process of this invention are uniform in appearance, rendering them suitable for immediate use in various applications. Where less dense layers are present, the total product has a regular geometry and the densified layer is uniform.

The flexible, densified polyurethane foams described herein are further characterized by having a Sac factor preferably between about 2.3 and about 10. Sac factor, as determined by ASTMl564-64T, is the ratio of 65 percent Indentation Load Deflection to .25 percent Indentation Load Deflection. The Sac factors of the densified polyurethane foams of this invention are high, and thus these foams have little tendency to bottom-out. The term bottoming-out is employed in the cushioning trade to describe a foam in which there is a sensation of sinking through and hitting the bottom when someone sits on it. Thus, it will be apparent that the densified,

polyurethane foams of this invention are highly useful for such applications as cushioning and rug padding.

In the preparation of the densified urethane compositions of this invention either the so-called one-shot method or the semi-prepolymer technique (quasiprepolymer technique) may be employed. Any combination of polyols, including polyether polyols and polyester polyols, organic polyisocyanate, foaming agent, catalyst and other reactants capable of forming a flexible urethane foam can be employed in carrying out the process of this invention, and the term polyurethane foam-forming reaction mixture in the specification and claims herein is meant to include any such combination, with the proviso that the polyurethane foam-forming reaction mixture has a free rise density between about 0.8 and about 4.0 pounds per cubic foot. Typical formulations are described in US. Patent No. 3,072,582, issued Jan. '8, 1963 and Canadian Patent No. 705,938, issued Mar. 16, 1965.

While, as indicated above, both polyether and polyester polyols can be employed in the practice of this invention, preferred embodiments utilize the polyether polyols in the preparation of the polyurethane foamforming reaction mixture. To further illustrate suitable formulations, the polyether polyols, useful for the preparation of the polyurethane material of this invention, include oxyalkylated polyhydric alcohols having a molecular weight in the range between about 700 and about 10,000 and preferably between about 1,000 and 6,000. The hydroxyl number of the polyether polyol is generally less than about 250 and preferably in the range between about 25 and about 175. These oxyalkylated polyhydric alcohols are generally prepared by reacting in the presence of an alkaline catalyst, a polyhydric alcohol and an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, epichlorohydrin, and mixtures of these alkylene oxides, by either random addition or step-wise addition.

Polyhydric alcohols suitable for use in preparing the polyether polyol include ethylene glycol, pentaerythritol, methyl glucoside, propylene glycol, 2,3-butylene glycol, 1,3-butylene glycol, 1,5-pentane diol, 1,6-hexane diol, glycerol, trimethylolpropane, sorbitol, sucrose, mixtures thereof and the like. If desired, a portion of all of the polyhydric alcohol may be replaced with another compound having at least two reactive hydrogen atoms, such as alkyl amines, alkylene polyamines, cyclic amines, amides, and polycarboxylic acids. Suitable alkyl amines and alkylene polyamines include methylamine, ethylamine, propylamine, butylamine, hexylamine, ethylenediamine, 1,6-hexanediamine, diethylenetriamine, and the like. Also, such cyclic amines as piperazine, .2-methylpiperazine and 2,5-dimethylpiperazine can also be used. Amides, such as acetamide, succinamide and benzenesulfonamide, constitute a further class of such reactive hydrogen compounds. A still further class of such reactive hydrogen compounds is the diand polycarboxylic acids, such as adipic acid, succinic acid, glutaric acid, aconitic acid, diglycollic acid, and the like. It will be recognized that the reactive hydrogen compound can be one containing different functional groups having reactive hydrogen atoms, such as citric acid, glycollic acid, ethanolamine, and the like. Aromatic polyamines such as toluene diamine can also be employed. Mixtures of oxyalkylated polyhydric alcohols are also suitable for use in the process of this invention.

The organic polyisocyanates used in the preparation of the densified urethane composition of this invention include toluene diisocyanate, such as the 4:1 mixture or the 65:35 mixture of the 2,4- and 2,6-isomers, ethylene diisocyanate, propylene diisocyanate, methylene-bis- 4-phenyl isocyanate, 3,3 bitoluene 4,4 diisocyanate, hexamethylene diisocyanate, naphthalene 1,5 diisocyanate, polyphenylene polymethylene isocyanate, mixtures thereof and the like. The amount of isocyanate employed in, the process of this invention should be sufiicient to provide at least about 0.7 NCO group per hydroxyl group present in the reaction system, which includes the polyol as well as any additive or foaming agent employed. An excess of isocyanate compound may be conveniently employed; however, this is generally undesirable due to the high cost of the isocyanate compounds. It is preferable, therefore, to employ sutficient isocyanate to provide no greater than about 1.25 NCO groups per hydroxyl group, and preferably between about 0.9 and about 1.15 NCO groups per hydroxyl group. The ratio of NCO to OH groups times is referred to as the index.

The partially cured polyurethane foams are prepared in the presence of a foaming agent, reaction catalysts, and preferably a small proportion of a conventional surfactant. The foaming agent employed may be any of those known to be useful for this purpose, such as water, as well as organic foaming agents containing up to about seven carbon atoms such as the halogenated hydrocarbons, lower molecular weight alkanes, alkenes, ethers and mixtures thereof. Typical halogenated hydrocarbons include, but are not limited to: monofiuorotrichloromethane, dichlorofluoromethane, difluorodichloromethane, 1,1,2-trichloro-1,2,2-trifiuoroethane, dichlorotetrafiuoroethane, ethyl chloride, methylene chloride, chloroform, and carbon tetrachloride. Other useful foaming agents include lower molecular Weight alkanes, alkenes and ethers such as methane, ethane, ethylene, propane, propylene, pentane, hexane, heptane, ethyl ether, diisopropyl ether, mixtures thereof, and the like. The amount of foaming agent employed may be varied within a wide range. Generally, however, the halogenated hydrocarbons are employed in an amount from about 1 to 50 parts by weight per 100 parts by weight of the polyol, and generally water is employed in an amount from about 1.0 to 6.0 parts by weight per 100 parts by weight of the polyol.

The partially cured polyurethane foams are prepared in the presence of a catalytic amount of a reaction catalyst. The catalyst employed may be any of the catalysts known to be useful for this purpose, or mixtures thereof, including tertiary amines and metallic salts, particularly stannous salts. Typical tertiary amines include, but are not limited to, the following: N-methyl morpholine, N- hydroxyethyl morpholine, triethylene diamine, triethylamine and trimethylamine. Typical metallic salts include, for example, the salts of antimony, tin and iron, e.g., dibutyltin dilaurate, stannous octoate, and the like. Any catalytic proportion of catalysts may be employed. Preferably, a mixture of amine and metallic salt is employed as the catalyst. The catalyst or catalyst mixture, as the case may be, is usually employed in an amount ranging between about 0.05 and about 1.5, and preferably between about 0.075 and about 0.50 percent by weight of the polyol.

It is preferred in the preparation of the polyurethane compounds of the present invention to employ minor amounts of a conventional surfactant in order to further improve the cell structure of the polyurethane foam. Typical of such surfactants are the silicone oils and soaps, and the siloxaneoxyalkylene block copolymers. US. Patent 2,834,748 and T. H. Ferrigno, Rigid Plastic Foams (New York: Reinhold Publishing Corp., 1963), pp. 38-42, disclose various surfactants which are useful for this purpose. Generally up to 2 parts by weight of the surfactant are employed per 100 parts of the polyol.

Various additives can be employed which serve to provide different properties, e.g., fillers such as clay, calcium sulfate, or ammonium phosphate may be added to lower cost and improve physical properties. Ingredients such as dyes may be added for color, and fibrous glass, asbestos, or synthetic fibers may be added for strength. In addition, plasticizers, deodorants and antioxidants may be added.

More in detail, in the practice of this invention a poly urethane foam-forming reaction mixture comprising the above-described ingredients is fed to a suitable reaction zone such as by pouring into a suitable box or into a moving conveyor belt where reaction proceeds. The foaming reaction is exothermic, and auxiliary heat is not necessary to effect the reaction, although it can, of course, be employed. After the reactants have been admixed for a period of between about 0.1 and about 20 seconds, an emulsion or cream forms. As the temperature increases from the reaction, gas bubbles are generated, which cause the formation of an uncured cellular gel material which gradually increases in volume.

After generation of gas bubbles is completed, the rise of the uncured cellular g'el material stops. The aforementioned critical process steps are employed at this point to provide densified foam compositions according to the teaching of this invention.

The first variable, which is referred to hereinafter as the crush time, is the period of time which elapses between the completion of the rise of the uncured foam and the first application of pressure to the partially cured foam to effect crushing of the foam. In the process of this invention, this period of time can vary from to about 10 minutes. While flexible, densified polyurethane foams can be provided immediately after completion of the rise, practical operations allow at least about 6 seconds to elapse prior to crushing.

The second critical variable is the temperature of the ambience during the crush time. During this period it has been found that the partially cured cellular material must be maintained within a critical environmental temperature range that is related to the crush time. Thus, where the crush time is between about 0 and about 2.5 minutes, temperatures between about 45 and about 400 F. and preferably between about 45 and about 200 F. are employed. Narrower temperature ranges are utilized where the partially cured cellular material is maintained for a longer crush time. Thus, where the time interval is between about 2.5 and about minutes, temperatures between about 45 and about 200 F. and preferably between about 45 and 100 F. are maintained, while temperatures between about 45 and 110 F. and'preferably between about 45 and about 85 F. are employed wherein about 5 to about 10 minutes elapse before the application of a compressive force tothe partially cured cellular material. Conventional means, such as ovens and cooling systems, are employed, if necessary, to provide the desired temperatures.

.In commercial operations, it is particularly preferred to operate under environmental conditions, and thus temperatures from about 70 to about 110 F. are employed therein while maintaining any crush time within the broad range of 0 to 10 minutes.

At the end of the crush time, the partially cured po yurethane foam is compressed by any suitable means, such as rollers, latens, and the like.

The degree of deflection effected by the application of the compressive force is also critical to the practice of this invention. It is necessary to compress the partially cured cellular material to between about Va and of its original thickness after rise in order to provide good densified foams. The desired degree of compression is achieved by adjusting the opening between the compressive means.

The duration of the crush and the temperature of the crushing means and the ambience during crushing are not critical to the practice of the invention described herein. However, it is apparent that commercial operations will avoid long crush durations for economic reasons.

After the partially cured polyurethane foam has been subjected to the pressure of the compressive means, the compressive force is removed and curing of the compressed material is completed. While curing can be accelerated by the application of heat, such treatment is not generally necessary since the foam will completely cure under ambient conditions. Thus, it will be recognized that completion of the cure can be effected with or without the use of elevated temperatures, and that both means are encompassed by the procedural step referred to in the description and in the claims herein as removing the compressive force and completing the cure of the compressed cellular material.

After removal of the compressive force and completion of the cure, the densified foam may recover a small portion of the difference between its intial height and the crushing gap, the degree of recovery depending upon the particular process variables. Of course, since the foam has been densified it is apparent that it never completely regains its original dimensions.

As previously indicated, the densified polyurethane foams of this invention may have top and/or bottom layers of less dense flexible polyurethane foam. In such a product, the densified portion comprises uniformly dispersed crushed cells; the entire product has a regular geometry. This type of product is useful for certain applications such as cushioning, and it can also be trimmed to remove the less dense material therefrom.

Where it is desired to decrease or eliminate the exterior low-density polyurethane layers from the product, certain formulation variations can be employed. Thus, for instance, it has been found that the use of one of the previously described fluorine-containing foaming agents causes a marked decrease in the thickness of the exterior lowdensity poly urethane layers.

However, when it is desired to prepare mattresses or cushions having a densified core surrounded by a relatively thick layer of light-weight polyurethane foam, then conditions are controlled to permit the increase of the thickness of the exterior layer. Mattresses, for example, preferably have an internal densified core of about 4 inches, and an exterior light-weight layer about 1 inch thick on the top and bottom.

When thin sheets having an insignificant exterior layer are produced continuously, substantially no trim is necessary, and after curing the sheets may be cut into any desired length. Similarly when compositions having a relatively thick exterior layer are used for mattresses, very little trimming of the exterior layer is necessary when the process conditions are properly controlled, and only cutting to length is necessary after the composition has been completely cured. However, if desired, the less dense exterior layer may be separated by cutting, shearing or the like, from the densified core, which then may be cut into sheets or other desired shapes, depending upon the ultimate use of the densified foam.

If desired, the flexible, densified polyurethane foam of this invention can be prepared batch-wise. An illustrative batch process comprises feeding the foam-forming ingredients into a conventional box, allowing the foam to complete the rise, permitting the crush time to expire while maintaining an environmental temperature within the previously described critical range, removing the box from the partially cured cellular material, and then applying compressive means thereto. Pressure is applied to the foam by means of platens or rollers to compress it to between about We and about of its original volume and then removed to permit the compressed foam to complete the cure.

However, it is preferred, particularly in commercial operations, to employ a continuous process for the preparation of the flexible, densified polyurethane foams of this invention. An exemplificative continuous process comprises admixing the foam-forming ingredients in a suitable mixing head and feeding the resulting mixture to a moving conveyor having suitable side retaining means to contain the liquid reactants. The side retaining means are necessary until the foam gels sufficiently to support its own weight. As the reaction proceeds while moving along the conveyor, bubbles form in the reaction mixture, which effects a volume increase and the formation of an uncured porous gel. After the uncured porous gel has traveled along the conveyor for a pre-determined crush time and at an appropriate enviromental temperature selected in accordance with the teachings of this invention, the resulting partially cured cellular material is passed between at least 2 rotating crushing rollers, or other appropriate compressive means. Suitable means for slitting the densified polyurethane foam may be installed at a further point along the conveyor.

Various modifications of the aforesaid process may be employed without departing from the spirit of this invention. For example, the densified urethane composition of this invention may be formed into backing for floor covering such as rugs, tiles, carpets and the like by pouring the reaction mixture directly onto the back of a continuous moving length of floor covering, and compressing the resulting partially cured cellular material. The exterior layer of low density porous urethane compositions may be separated :by cutting or shearing, but if desired, it may be retained as part of the backing of the floor covering.

As indicated above, the flexible, densified polyurethane foams of this invention have a wide variety of applications. Thus, for example, they are particularly valuable in the following areas: innersoles and liners for shoes; as backing, either as an integral part or a separate layer, for floor tiles made of rubber, asphalt, vinyl asbestos, vinyl, linoleum, chlorinated polyethylene elastomer, etc.; carpet backing and padding, either as an integral part or a separate layer, for carpets or rugs including wool, nylon, cottion, rayon, Acrilan, polypropylene, and other types; mattresses; cushions; and furniture upholstery and construction.

Furthermore, they are useful for gasketing; padding applications of all types including floor pads for use in occupations requiring prolonged standing, table pads or table pad construction, key pads for musical (reed) instruments, and packaging uses for delicate instruments; belting uses, particularly where chemical resistance is important; special filter media; weather-stripping; vibration insulators, including motor mounts; gymnastic equipment; hammers for piano construction; solid tires for fork-lifts, etc.; roofing systems, including use in laminates such as with chlorinated polyethylene; underlay for flooring materials; backing for floor sheeting materials as an integral part of the sheet; padding and case liners for delicate instruments; and industrial roll covering.

Other suitable applications for the flexible, densified polyurethane foams of this invention include elastorneric hammer heads; bottle cap liners; bulletin board construction; sealant gaskets, such as for drums, pails and other containers; wear-resistant stair treads and heavy-trafficarea fioor covering; bumpers for loading docks and similar uses; blackboard erasers; squeegees for various applications; windshield wipers; door mats; skid-resistant, marresistant sheeting for underlining lamps, desk accessories, vases, appliances, etc.; pressure-sensitive tapes; phonograph turntable cushioning; automotive pedal covers; recoil pads for firearms; and automotive padding.

The following examples are presented to illustrate the invention more fully without any intention of being limited thereby. All parts and percentages are by weight unles otherwise specified.

EXAMPLES l-3 A conventional, low-pressure, four-stream foam machine capable of pouring foam formulations was provided with a polyether polyol (a blend of parts of oxypropylated glycol, molecular weight of 2000, per 85 parts of oxyalkylated glycerin obtained by oxypropylating glycerin to a molecular weight of 3700 followed by topping with five mols of ethylene oxide), toluene diisocyanate, water, catalysts, surfactant and chlorinated hydrocarbon. The feed rate was adjusted to provide a foam formulation with the following ingredients in the following proportions.

Ingredients: Parts by weight Polyether polyol blend 100 Triethylene diamine 0.15

Silicone surfactant (General Electric 81 1034) 2.45

Trichloromonofiuoromethane 10.0

Stannous octoate 0.2

Water 4.5 Toluene diisocyanate 2,4-, 20% 2,6-

isomer; 105 index) 52.5

1 This silicone surfactant is a block copolymer of a dimethyl polysiloxane and a polyalkylene oxide. The polyalkylene oxide is a random linear copolymer consisting of 50 weight percent ethylene and 50 Weight percent propylene oxides terminated with a hutoxy group. The branched polysiloxane and each of the polyether blocks have a molecular weight of 1500 to 1300.

This foam formulation, which had a free rise density of about 1.0 pound per cubic foot, was utilized to prepare three foams, further identified as Examples 1, 2 and 3, respectively, in accordance with the following procedure. The reaction mixture wa dispensed from the foaming machine into a square box having side dimensions of 16" and a height of 8". After bubbles appeared on the surface of the foam indicating the completion of the rise, the box was cut and the foam was removed and covered with brown paper on the top and bottom. This operation required approximately 30 seconds; the temperature of the environment was about 75 F. After allowing the foam to remain for an additional seconds under these conditions, the foam sample was passed through rotating crusher rolls set at various openings as indicated in the table below.

Foam Foam Thick- Density height height; ness of 0 before Roll after densified densified crush opening crush layer layer Example (in) (in.) (in.) on.) (p.c.f.)

EXAMPLES 46 The procedure of Examples 13 was repeated employing the following ingredients in the following proportions.

Ingredients: Parts by weight Oxypropylated glycerin (molecular weight 3000) Trichloromonofluoromethane 20 Silicone surfactant of Examples 1-3 2.0 Stannous octoate 0.22

Water 4.0 Triethylene diamine 0.10 Toluene diisocyanate (80% 2,4-, 2,6-isomer 101-index) 46.1

This foam formulation, which had a free rise density of about 1.0 pound per cubic foot, was utilized to prepare three foams, which are identified as Examples 4, 5, and 6, respectively. Each foam, after the rise had been completed, was maintained at room temperature (about 75 F.) for a crush time of 120, 75, and 45 seconds, respectively, prior to the application of the compressive force. The data for these examples is reported in the following table.

Foam Foam Thiek- Density height height ness of of before R after densified densified crush height crush layer layer Example (111.) (in.) (in.) (in (p.f.c.)

9 l 1 "If s l). 1

9 EXAMPLES 7-10 A polyurethane foam-forming reaction mixture was prepared from the following ingredients in the following proportions.

Silicone surfa'ctant (Dow Corning DC-190) 1.5

This s urfacbant is a block copolymer of a polydimethylsiloxane and a polyether resin.

The foam formulation was utilized to prepare four foams, identified as Examples 7, 8, 9, and 10, respectively. In Example 7 the above-identified formulation was used to prepare the foam. In Examples 8, 9, and 10, five parts, ten parts and fifteen parts, respectively, of trichloromonofluoromethane were added to the above-identified formulation prior to forming the foam. The formulation of Examples 7-10 were then each poured into a square box having side dimensions of about 12 inches and a height of about 6 inches. After the rise was completed, a crush time of 90 seconds (environmental temperature 75 F.) was allowed to elapse, and then the foam was crushed between platens on a hand press set at an opening of about 1.5 inches. The resulting foams were then measured for the thickness of the densified layer and exterior layers, and analyzed for density and strength. The results are set forth in the table below.

Example 7 Parts of trichloromonofluoromethane.. Free rise density of formulation, p.c.f 1. 5 1. 35 1. 2 1.1 Undensified layers, thickness, inches:

T A6 "lie @in its 0 0 0 Total /8 it a 5i 0 4 Densified layer thickness, inehe 1% V0 1% 1% Total sample height, inches 1% 1% M6 1% Density of densified layer, p.c.f 5. 41 5. 54 5. 67 5. 79 Sac factor 66 5. 79 5. 93 5. 84 Tensile strength, p.s.i ASTM D1564- 59T, Sections 53-58 53.2 56. 1 64. 1

EXAMPLES 11-12 Two foam formulations, each similar to Example 7, were each used to form a foam in a square box having side dimensions of about 18 inches and a height of about 12 inches. After allowing both foams to remain at 75 F. for 90 seconds after completion of rise, they were passed through crushing rollers. Each original foam had a height of about 12 inches prior to crushing. The resulting densified foams are identified below as Examples 11 and 12, respectively.

Item Example 11 Example 12 Roller opening, in 3 3. 65 Crushed height, in 3% 5 Thickness of densified layer, in 3 4 Density, outer layers/densified layer (p. .f.) 1. 5:4. 9 1. 5:3. 2 25 percent indentation load deflection, lbs 64 46 Sac factor 6. 0 5.0

EXAMPLE 13 10 of 1.9 pounds per cubic foot; the final height of the foam after curing was 3.3 inches.

EXAMPLES 14-15 A polyurethane foam-forming reaction mixture was prepared from the following ingredients in the following proportions.

Ingredients: Parts by weight Oxypropylated glycerin (molecular weight 3000 10o Toluene diisocyanate (80% 2,4-, 2,6-isomer; 105 index) 34.3 Stannous octoate 0.20 Triethylene diamine 0.10 Water 4.0 Silicon surfactant, of Examples 7-10 1.5

This foam formulation, which had a free rise density of 1.5 pounds per cubic foot, was utilized to prepare two densified polyurethane foams, identified as Examples 14 and 15 respectively. Each original foam had a height of about four inches and was compressed to a height of one inch. The foam represented by Example 14 was crushed 12 seconds after completion of rise while a crush time of 6 seconds was employed to prepare the foam of Example 15. The temperature of the ambience during the crush time was approximately 75 F. for both foams. Uniformly densified polyurethane foams of excellent quality were obtained. The foam represented by Example 14 had a density of 7.2 pounds per cubic foot, while the foam of Example 15 had a density of 6.8 pounds per cubic foot; both foams had a final height of one inch.

EXAMPLE 16 A polyurethane foam-forming reaction mixture was prepared from the following ingredients in the following proportions.

Ingredients: Parts by weight Oxypropylated glycerin (molecular weight 3000) Toluene diisocyanate (80% 2,4-, 20% 2,6-isomer; 105 index) 39.4 Stannous octoate 0.20 Triethylene diamine 0.10 Trichloromonofluoromethane 20.0 Water Silicone surfactant of Examples 7-10 Following the procedure of the previous examples, the resulting mixture, which had a free rise density of about 1.1 pounds per cubic foot, was poured and allowed to rise to a height of 5 inches. After completion of the rise, the foam was placed in an oven heated to 110 F. for 10 minutes. At the end of this period, the partially cured cellular material was crushed to a height of 0.5 inch. After removal of the compressive force, a uniformly densified polyurethane foam having flat, smooth surfaces, 21 total thickness of approximately 0.5 inch and a density of 9.6 pounds cubic foot was obtained.

EXAMPLE 17 A polyurethane foam-forming reaction mixture similar to that of Example 16 was employed to prepare a densified polyurethane foam as described in the previous exam- 65 ples. An environmental temperature of 400 F. was maintained during the 2-minute crush time and the resulting partially cured cellular material was compressed from an original height of 5 inches to 1.25 inches. A uniformly densified polyurethane foam having a height of 1.25 inches 7 and a density of 4.4 pounds per cubic foot was obtained.

EXAMPLE 18 A flexible polyester based polyurethane foam formulation was prepared by admixing the following ingredients in the following proportions.

11 Ingredients: Parts by weight Polyester of adipic acid, trimethylol propane and diethylene glycol (corrected hydroxyl amples 1-10. Where densification occurred, the foams were irregularly shaped, with non-uniform internal bands of densified foam. A densified polyurethane foam was number 45-52) 100 also produced according to this invention, employing the Toluene diisocyanate (80% 2,4-, 20% 2,6-isosame formulation as Comparative Example 4. In contrast, mer) 53.5 a this polyurethane foam, described in detail in Example N-ethylmorpholine 2.0 20, was a uniformly densified material having a regular Water 4.3 geometry. Ammonium oleate 1.5 In Comparative Example 1, a polyurethane form-form- Coupling agent (Witco FOMEZ 77-86 noning reaction mixture was prepared from the following inionic/anionic surfactant blend containing gredients in the following proportions. g 3 12 1 gtzgfig iigg and esters and 1 5 Ingredients: Parts by weight Oxypropylated glycerin (molecular weight Following the procedure of the previous examples, a 3000) ".7 100 densified polyurethane foam was prepared employing a Toluene dnsoc.yanate (80% crush time of 90 seconds at an environmental temperalsomer 110 Index) 35 ture of 150 F. The foam was compressed from an origistimllous i f nal height of about four inches to one inch. A uniformly gh i densified polyurethane foam having smooth surfaces, a 20 i yene dlamme "'1 height of one inch and a density of 7 7 pounds per cubic slhcone slufactant (Unlon Carbide L420;

organo-silicone fluid) 1.0 foot was obtained. We}ter 2 9 For purposes of comparison, the procedure was repeated with the exception that the mixture was allowed to cure comparatlve mples 24, the ingredients and proin a conventional manner without crushing. A typical Pomons of Comparanve Example 1 were 53d, but the polyester flexible foam having a density of 1.64 pounds lsfocyzlmate cofltent was vaned; parts by Welght per cubic foot and a height of 4 inches was thereby obo to uene (.insoganate were used m Example 38 mined. parts by welght 1n Example C-3, and 41 parts by weight EXAMPLE 19 1n Example C-4.

Example 20 was carried out employing the same for- Ingredients: Parts by weight mulation as Example C-4 and the process conditions of Oxypropylated glycerin (molecular weight this invention.

3000) 100 Employing the formulation of Example C-3, the crush Toluene diisocyanate (80% 2,4-, 20% 2,6- time was varied in Comparative Examples 5-8.

isomer; 105 index 49.5 A formulation identical to the formulation of Example Stannous octoate 0.375 20 and Comparative Example 4, with the exception that Triethylene diamine 0.1 3.4 parts by weight of water were used, was employed in Silicone surfactant of Examples 7-10 2.0 Comparative Examples 9 and 10. Water 4.0 The process variables and roperties of the resulting Trichloromonofiuoromethane 30.0 polyurethane foams are tabulated below:

Temp. Foam height Foainheight Crush time during crush before crush Percent deafter crush Example (min.) time F.) (in.) fiection (in.) Geometry of foam Degree of densification C-l 30 150 2.5 90 2.5 Fairly regular None. 02 30 150 2. 5 90 1.3-2. 4 Dumbell-shaped; uneven surfaces- Barely perceptible at top of C-3 30 150 2.5 90 1. 323 do Dii ifihii incenter. C-4 30 150 2. 5 90 1. 2-2. 1 do Densified with hard band at top. 20 1. 5 110 2. 5 0. 95 Uniform; regularly shaped; even Uniformly densified; 5.20 p.c.f. C-5 12 150 2.5 1.1-1.7 Diiin ligl l shaped; uneven surfaces. Highly densified. C-6 20 150 2.5 90 1. 4-23 1 Do. C-7 30 150 2. 6 90 1.8-2.6 d0 Some densification at top. C-8 60 150 2.8 90 2.8 Fairly regular uneven surfaces. No densification. c-0 17 150 3.5 75 3.4 o None. C-iO 19 150 3. 5 1. 9-2. 7 Dumbellshaped; uneven surfaces- Densification in center band.

The mixture, which had a free rise density of 0.88 For further purposes of comparison, highly densified pound per cubic foot, was poured and allowed to rise polyurethane foams were made according to the teachto a height of 6 inches. The foam was crushed secings of US. Patent 3,125,617; these materials, described onds after completion of the rise to 2.4 inches; the temin the following comparative examples, were found to be perature of the ambience during the crush time was ap- 65 unsuitable for use as rug padding. proximately 75 F. After removal of the compressive COMPARATIVE EXAMPLE 11 force, a uniformly densified polyurethane foam having a height of about 2.4 inches and a density of 1.67 pounds 100 parts of 11 Polyester Were P p from 25 mols Per bi f t was b i d 8f adipic a iid ,r0.5 mols of phthalic acid, and 4 mols of 70 exane trio he polyester was heated to C., and COMPARATIVE EXAMPLES 2.5 parts of pulverized 1,5-naphthalene diisocyanate were For purposes of comparison, polyurethane foams were introduced. The components were thoroughly mixed until made following the teachings of Mobay Chemical Co. the diisocyanate had melted completely and the mixture Technical Information Bulletin TIB No. 38-F 14, dated gelled to a clear amber-colored solid. Upon gelling, the Nov. 25, 1959; this data is set forth in Comparative Ex- 75 temperature rose from 135 C. to C. The solid mix- 13 ture was allowed to cool to 75 C. and one part water and 0.5 part of hexahydro dimethyl aniline were introduced. Because the mixture had solidified, 110 mixing was possible and no foaming occurred; a rigid, solid, resinous mass was obtained.

COMPARATIVE EXAMPLE 12 100 parts of a polyester prepared from 11 mols of ethylene glycol and mols of adipic acid was heated to 140 C. Twenty-five parts of 1,5-naphthalene diisocyanate were added to the heated polyester with intense mixing while the diisocyanate melted. After mixing for about 10 seconds, 2 parts of activator consisting of one part sodium phenate and 9 parts dibutyl phthalate were introduced. After mixing once more for about 7 seconds, the foaming process began. A polyurethane foam having a free rise density of 25 pounds per cubic foot was obtained.

In order to obtain a foam having a densified volume of 25 pounds per cubic foot, it was necessary to heat the polyester to 175 C.; in this procedure, the plunger was applied as soon as foaming of the ingredients had finished.

COMPARATIVE EXAMPLE 13 Comparative Example 13 was carried out following the procedure of Comparative Example 12, except that the plunger was applied immediately after the activator and the diisocyanate components were mixed into the polyester component at the onset of foaming. The foaming process was carried out in a closed mold against a stationary plunger; a highly densified polyurethane foam was obtained.

COMPARATIVE EXAMPLE 14 100 parts of the polyester described in Example 1 was heated to 135 C. and 25 parts of p-phenylene diisocyanate was introduced. The components were thoroughly mixed until the diisocyanate had melted completely; the mixture immediately gelled to a clear amber-colored solid. Upon gelling, the temperature of the mixture rose from 135 C. to 180 C. The solid mixture was allowed to cool to 75 C. At 75 0, one part water and 0.5 part of the adipic ester of N-diethyl amino ethanol were introduced.

Because the mixture had solidified, no mixing was possible and no foaming occurred. A rigid, resinous mass similar to that of Comparative Example 11 was obtained.

In order to demonstrate the superior properties of the densified polyurethane foams of this invention, the foams of Comparative Examples 12 and 13, and a polyurethane foam having a density of 5.9 pounds per cubic foot produced according to the process of this invention, were tested for use as rug padding. The basic equipment and procedure followed in this test is described by H. Schiefer in Wear Testing of Carpets, Research Paper RP1505, Journal of Research of the NBS, vol. 29, November 1942; an NBS machine was employed.

The densified polyurethane foam was produced according to the procedure of Examples 1-3; the feed rate of the foam machine was adjusted to provide a foam formulation with the following ingredients in the following proportions.

hydroxyl groups) This formulation, which had a free rise density of 1.5 pounds per cubic foot, was allowed to rise to a height of 25 inches. Employing a crush time of 113 seconds, the foam was passed through crusher rolls having an opening of 4.2 inches. A densified polyurethane foam having a height of 6.5 inches and a density of 5 .9 pounds per cubic foot was obtained.

Briefly, the test machine consists of a motorized, horizontal turntable operated at rev/min. and a vertical wheel, which rolls on the turntable, thereby producing a wear track on the material covering the turntable. The vertical wheel rolls at 56 rpm. and is loaded by a weight and lever to have a plate pressure of 420 pounds and a brake pressure of 16 pounds. The test was conducted in a controlled-atmosphere room having a temperature of about 75 F. and a relative humidity of about 50%.

A fii-inch thick disc of the aforementioned densified polyurethane foam of this invention was cut to cover the turntable. Three circular disc, approximately 3 /2 inches in diameter, were cut from the large disc at equidistant points along the intended wear track. Two of the apertures were filled in with discs of the foams of Comparative Examples 12 and 13 and one was replaced with the disc of polyurethane foam originally cut from it. Then the large disc containing the samples to be tested was placed on the turntable and covered with nylon Axminster carpet having a 5 lines/inch backing. After 10,000 cycles of the turntable, visual examination revealed that the material of Comparative Examples 12 and 13 had deep ridges and extremely irregular surfaces. Contrary to these samples, the densified polyurethane foam of this invention showed little evidence of wear; the surface having a wear track was still smooth to the touch.

What is claimed is:

1. A process for preparing a flexible, densified po1y urethane foam having a density between about 1.5 and about 15 pounds per cubic foot which comprises (a) placing a polyurethane foam-foaming reaction mixture having a free rise density between about 0.8 and about 4.0 pounds per cubic foot in a reaction zone and allowing the mixture to rise, thereby forming a partially cured cellular material;

(b) applying a compressive force to the partially cured cellular material after the elapsing of a period of time between 0 and about 10 minutes after completion of the rise, thereby (c) reducing the volume of the partially cured cellular material to between about and about of its original volume; and

(d) removing the compressive force and completing the cure of the compressed cellular material with the proviso that where the period of time between completion of the rise and application of the compressive force is between 0 and about 2.5 minutes, the partially cured cellular material is maintained at an environmental temperature between about 45 and about 400 F. for said period;

where said period of time is between about 2.5 and about 5 minutes, the partially cured cellular material is maintained at an environmental temperature between about 45 and about 200 F. for said period; and

where said period of time is between about 5 and about 10 minutes, the partially cured cellular material is maintained at an environmental temperature between about 45 and 110 F. for said period.

2. The process of claim 1 wherein a flexible, densified polyurethane foam having a density between about 1.5 and about 10 pounds per cubic foot is provided.

3. The process of claim 1 wherein the partiall cured cellular material is maintained at an environmental temperature between about 45 and about 200 F. where the period of time between completion of the rise and application of the com pressive force is between 0 and 2.5 minutes;

45 and about F. where said period of time is between about 2.5 and about 5 minutes; and

45 and about 85 P. where said period of time is between about 5 and about 10 minutes.

4. The process of claim 1 wherein the compressive force is applied to the partially cured cellular material after the elapsing of a period of time between and about 10 minute after completion of the rise and where said partially cured cellular material is maintained at an environmental temperature between about 70 and about 110 F. for said period.

5. The process of claim 1 wherein said polyurethane foam-forming reaction mixture comprises a polyether polyol.

6. The process of claim 5 wherein said polyether polyol is an oxyalkylated polyhydric alcohol having a molecular weight in the range between about 700 and about 10,000.

7. The process of claim 6 wherein said polyether polyol is oxypropylated glycerin.

8. The process of claim 5 wherein the foaming agent employed in the preparation of said polyurethane foamforming reaction mixture is water.

9. The process of claim 8 wherein the reaction catalyst employed in the preparation of said polyurethane foamforming reaction mixture is a mixture of an amine and a stannous salt.

10. The process of claim 5 wherein the foaming agent employed in the preparation of said polyurethane foamforming reaction mixture is a mixture of water and an organic foaming agent.

11. The process of claim 10 wherein the reaction catalyst employed in the preparation of said polyurethane foam-forming reaction mixture is a mixture of an amine and a stannous salt.

12. The process of claim 1 wherein said polyurethane foam-forming reaction mixture comprises oxypropylated glycerin having a molecular weight in the range between about 1,000 and about 6,000, toluene diisocyanate, water and a mixture of an amine and a stannous salt.

13. A continuous process for preparing a flexible, densified polyurethane foam having a density between about 1.5 and about pounds per cubic foot which comprises (a) continuously feeding a polyurethane foam-forming reaction mixture having a free rise density between about 0.8 and about 4.0 pounds per cubic foot to a moving reaction zone having side-retaining means and allowing the mixture to rise, thereby forming a partially cured cellular material;

(b) conveying said partially cured cellular material through compressive means after the elapsing of a period of time between 0 and about 10 minutes after completion of the rise; thereby (c) reducing the volume of the partially cured cellular material to between about /a and about of its original volume and (d) removing said cellular material from said compressive means and completing the cure of the compressed cellular material with the proviso that where the period of time between completion of the rise and application of the compressive force is between 0 and about 2.5 minutes, the partially cured cellular material is maintained at an environmental temperature between about 45 and about 400 F. for said period;

where said period of time is between about 2.5 and about 5 minutes, and partially cured cellular material is maintained at an environmental temperature between about 45 and about 200 F. for said period; and

where said period of time is between about 5 and about 10 minutes, the partially cured cellular material is maintained at an environmental temperature between about 45 and 100 F. for said period.

14. The process of claim 13 wherein a flexible, densified polyurethane foam having a density between about 1.5 and about 10 pounds per cubic foot is provided.

15. The process of claim 13 wherein the compressive force is applied to the partially cured cellular material after the elapsing of a period of time between 0 and about 10 minutes atfer completion of the rise and where said partially cured cellular material is maintained at an environmental temperature between about and about F. for said period.

16. The process of claim 15 wherein said polyurethane foam-forming reaction mixture comprises a polyether polyol.

17. The process of claim 16 wherein said polyether polyol is an oxyalkylated polyhydric alcohol having a molecular weight in the range between about 700 and about 10,000.

18. The process of claim 17 wherein said polyether polyol is oxypropylated glycerin.

19. The process of claim 16 wherein the foaming agent employed in the preparation of said polyurethane foamforming reaction mixture is water.

20. The process of claim 19 wherein the reaction catalyst employed in the preparation of said polyurethane foam-forming reaction is a mixture of an amine and a stannous salt.

21. The process of claim 15 wherein said polyurethane foam-forming reaction mixture comprises oxypropylated glycerin having a molecular weight in the range between about 1,000 and about 6,000, toluene diisocyanate, water and a mixture of an amine and a stannous salt.

22. The process of claim 2 wherein the compressive force is applied to the partially cured cellular material after the elapsing of a period of time between 0 and 10 minutes after completion of the rise, and where said partially cured cellular material is maintained at an environmental temperature between about 70 and about 110 F. for said period.

23. The process of claim 22 wherein said polyurethane foam-forming reaction mixture comprises oxypropylated glycerin having a molecular weight in the range between about 1,000 and about 6,000, toluene diisocyanate, a surfactant, water and a mixture of an amine and a stannous salt.

24. The process of claim 23 wherein said polyurethane foam-forming reaction mixture also contains a halogenated hydrocarbon as a foaming agent.

25. The process of claim 14 wherein the compressive force is applied to the partially cured cellular material after the elapsing of a period of time between 0 and about 10 minutes after completion of the rise, and where said partially cured cellular material is maintained at an environmental temperature between about 70 and about 110 F. for said period.

26. The process of claim 25 wherein said polyurethane foam-forming reaction mixture is poured directly onto the back of a continuously moving length of fioor covering and the resulting partially cured cellular material is compressed thereon.

References Cited UNITED STATES PATENTS 12/1961 Foster 26454 9/1968 Le Roy 264321 U.S. Cl. X.R. 2602.5; 264321 

